I’m Covid Antibody Negative Despite Being Fully Vaccinated; Is That a Problem?

A physician looks at how our immune systems respond to the Covid vaccine

Bo Stapler, MD
Medium Coronavirus Blog
3 min readApr 9, 2021

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Photo: RF._.studio/Pexels

I received my second dose of the Pfizer-BioNTech Covid-19 vaccine on January 4th of this year. I donated blood on March 19th. The donation center routinely checks for antibodies to Covid-19 in their donors. To my surprise, I was antibody negative. Does that mean my vaccine didn’t work?

The short answer is, “no.” Here are two reasons why I’m not concerned, and if you find yourself in a similar situation, you need not worry either.

1) Antibody tests aren’t perfect

Not all antibody tests are the same. There are a number of different classes of antibodies or immunoglobulins (Ig). For instance, IgM is made by the body early in the course of an illness, but levels of IgM decline sharply within days to weeks. On the other hand, IgG antibodies aren’t produced until later in the course of an illness but tend to last for months, or even years, after an infection has resolved.

Image courtesy of Wikimedia, Creative Commons

Furthermore, the body manufactures antibodies to many different viral proteins, also called antigens. An individual who was previously infected with the novel coronavirus, SARS-CoV-2, may possess antibodies, for example, to the nucleocapsid antigen but perhaps not to the envelope antigen. So, if a test is performed that only measures antibodies to the envelope antigen, then the result in this example would be a false negative.

The Covid vaccine stimulates the body to produce antibodies only to the spike protein and not to other parts of SARS-CoV-2. That means for a vaccinated patient who never had a natural infection, testing for antibodies to proteins other than the spike would produce a negative result.

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Bo Stapler, MD
Medium Coronavirus Blog

Health & science writer on Elemental & other pubs. Hospitalist physician in internal medicine & pediatrics. Interpreter of medical jargon. bostapler.medium.com